Anal Cancer Prevention (PDQ®)

Overview

Who Is at Risk?

Human papillomavirus (HPV) infection is the strongest risk factor for anal cancer and is accepted as a causal agent of squamous cell carcinoma of the anus and its precursor lesions.[1] Behaviors or medical conditions that either indicate HPV infection or facilitate HPV transmission or persistence are associated with increased risk; these include history of HPV-related cancers, high-risk sexual practices such as sex between men, receptive anal intercourse and numerous sexual partners, human immunodeficiency virus (HIV) infection, and chronic immunosuppressive states.[2] Cigarette smoking is also a risk factor.[3]

Factors Associated With Increased Risk of Anal Cancer

Anal HPV infection

Based on solid evidence, HPV infection causes squamous cell carcinoma of the anus.

Magnitude of effect: About 90% of anal squamous cell cancers occur in individuals with detectable HPV infection.[4] Of those, HPV strain 16 (HPV-16) and/or HPV-18 are detectable in more than 90% of cases.[4] Eighty-five percent of anal cancers have squamous cell histology.[2]

Behaviors or medical conditions that either lead to HPV infection or facilitate HPV transmission or persistence

Based on solid evidence, behaviors or medical conditions that either indicate HPV infection or facilitate HPV transmission or persistence increase the risk or are associated with increased risk of anal cancer.

Magnitude of effect: Risk varies by behavior and medical condition.

History of cervical, vaginal, and vulvar cancer increases risk at least threefold.[5-8]

High-risk sexual practices increase risk at least twofold, higher for persons with many sexual partners and those who partake in receptive anal intercourse.[3,9-11]

Chronic immunosuppressive states increase risk about 30-fold for persons who are HIV positive, and risk is much higher for men who both are HIV positive and have sex with men.[12]

Risk is at least threefold higher for organ transplant recipients.[11]

Study Design: Cohort, cancer registries, case-control studies.

Internal Validity: Good.

Consistency: Good.

External Validity: Good.

Cigarette smoking

Based on solid evidence, cigarette smoking increases the risk of anal cancer.

Magnitude of effect: Risk is about twofold to threefold for ever-smokers; current smokers are at higher risk.[3,11,13]

Study Design: Cohort, case-control.

Internal Validity: Good.

Consistency: Good.

External Validity: Good.

Interventions Associated With a Decreased Risk of Anal Cancer

HPV vaccination

Based on solid evidence, HPV vaccination of men aged 16 to 26 years who have sex with men in the year before vaccination reduces anal intraepithelial neoplasia (AIN), a precursor lesion of anal cancer.

Magnitude of effect: Vaccine efficacy against HPV-6, -11, -16, or -18–related AIN is between 50% and 75%.[14] Efficacy may be highest in those who are negative for the four HPV strains at the time of vaccination.

Study Design: Randomized controlled trial.

Internal Validity: Good.

Consistency: Not applicable (N/A)—only one study.

External Validity: Good.

Interventions With Inadequate Evidence as to Whether They Reduce the Risk of Anal Cancer

Condom use

In a study of HPV transmission, men who have sex with men (MSM), had recently had anal sex, and never use condoms were more likely to be infected with oncogenic HPV strains than were those who always used condoms. However, the association was not statistically significant.

Nyitray AG, Carvalho da Silva RJ, Baggio ML, et al.: Age-specific prevalence of and risk factors for anal human papillomavirus (HPV) among men who have sex with women and men who have sex with men: the HPV in men (HIM) study. J Infect Dis 203 (1): 49-57, 2011. [PUBMED Abstract]